Liquid fuel portable heater and control method of said heater

ABSTRACT

A liquid fuel portable heater (100) comprises: a combustion chamber (101) having a fuel inlet with a nebuliser (13); an electric pump (10) having an inlet (11) for suctioning said liquid fuel from a tank (6), and an outlet (12) connected to said nebuliser (13); a control unit (20) configured so that, when the heater (100) is turned on, said control unit (20) supplies the electric pump with a sequence of pulses (115, 115′) with a non-zero voltage, and pause intervals (116) with a substantially zero voltage alternating with said pulses, wherein the average duration of the pulses (115, 115′) is less than the average duration of the pause intervals (116). In addition, a method for controlling an electric power supply of a fuel electric pump (10) of a liquid fuel portable heater by means of an electric control unit (20) configured to control said electric power supply, comprising a step of electrically supplying said pump, once the heater is turned on, with a sequence of pulses (115, 115′) with a non-zero voltage, and pause intervals (116) with a substantially zero voltage alternating with said pulses, wherein the average duration of the pulses (115, 115′) is less than the average duration of the pause intervals (116).

SCOPE OF THE INVENTION

The present invention relates to a liquid fuel portable heater optimisedto reduce the consumption of electricity needed for it to operate.

STATE OF THE ART

Liquid fuel portable heaters generally comprise a fuel tank and acombustion chamber into which a fuel aerosol is introduced, taken fromthe fuel tank, which is nebulised through a nozzle nebulizer. Such knowndevices use an electric pump to withdraw the liquid fuel from the tankand bring it to the nebulizer nozzle at a preset pressure. Said heatersmay further comprise further electrical devices needed to operate, suchas a fan to convey the combustion air into the combustion chamber or todiffuse heated hot air from the combustion chamber into the environment.Solenoid valves, safety systems, electrical controls, requiringelectricity to operate may also be present,

Said known heaters therefore require a significant supply of electricityto operate all the internal electrical devices, among which theaforesaid electric pump.

By way of example, a typical heater with a thermal power output of 20kW, or 68,200 BTU/h, may require electrical power of indicatively 50 Wto operate its electrical equipment, about half of which is needed tooperate the pump alone.

Conversely, in order to facilitate moving or transporting the portableheater, and in order to use the heater in places where there is no mainselectricity, connection cables to the mains need to be avoided to permitstandalone operation of the heater.

To meet this need, attempts have been made to develop heaters which havea source of electricity on board, such as electric batteries orconverter devices of the temperature difference between the combustionchamber and the external environment into electricity, such as forexample thermoelectric cells, making the operation of the heaterindependent of the mains electricity supply.

Since the amount of electricity required by the known heaters is veryhigh, the known heaters require high-capacity and therefore very bulkyand heavy batteries.

Furthermore, in the case of using thermoelectric cells to convertthermal energy into electricity, it would be necessary to install a verylarge number of cells on board, requiring extensive support surfacesaround the combustion chamber to house them, entailing very largedimensions of the heater and a consequent increase in costs.

These technical limitations conflict with the need to provide a smallsize and lightweight portable heater with a high autonomy of operation.

Consequently, to reduce the size and weight of the heater, the need isstrongly felt to reduce the consumption of electricity absorbed by theelectric devices on board, among which the electric pump for liquid fuelwhich powers the burner of the heater.

Said pump is used to generate a pressure of liquid fuel upstream of anebulizer nozzle high enough to nebulise the fuel through the nebulizer.

At said pressure the nozzle nebulises the fuel by generating an aerosolwith the combustion air, thus feeding the combustion of the flametriggered by an ignition system.

The flow capacity of the pump must be equal to or greater than theoutput flow from the nebulizer nozzle, at a given pressure. A drop incapacity would in fact lead to a consequent decrease in pressure and theloss of the correct amount of fuel nebulised.

The typical pumps for burners used according to the prior art,classified by flow and pressure, are usually over-sized in order tocater to a wide range of sizes of burners to which they can be fitted.

This over-sizing is materialised in excessive work by the pump, wellabove the actual needs of the system; said extra work is dissipated inthe form of recirculation and discharge of the surplus flow upstream ofthe pump.

The power consumption of the pump is obviously related to how much flowit is able to deliver at a certain pressure, obviously net of output andpressure drops.

In light of the above, and in particular of the fact that the pumpsfitted on known heaters are typically oversized in relation to actualneeds, it follows that these heaters have a significantly higherelectrical consumption than necessary, weighing heavily on the operativepower reserve of battery-powered heaters or on the size thereof or onany self-generating electrical devices, such as thermoelectric cells.

With reference to a typical flow-pressure trend of a pump generally usedin the prior systems, for example shown in FIG. 1A, where the pressureis shown on the x-axis and the flow on the y-axis, a system using only aportion of such performance merely uses these curves at a certainpressure, diverting the excess flow and thus wasting the electricityconsumed.

For example, if a portable heater is designed to be powered by nebulisedfuel at 8 bar, thus consuming 2 litre/hours of fuel, and is fitted witha pump the characteristic curve of which shows a flow of 20 litre/hoursat 8 bar, it follows that about 9/10 of the electricity consumed topower said pump is unnecessary, the fuel being mainly discharged and notintroduced by the nebulizer for combustion.

The need is therefore felt to reduce the consumption of electricityabsorbed by the pump, and in the case of an over-sized pump being used,to avoid the need to divert the excess flow of fuel back towards thetank.

SUMMARY OF THE INVENTION

A purpose of the present invention is to make available a liquid fuelportable heater which makes it possible to satisfy the above needs andat least partially overcome the drawbacks mentioned with reference tothe prior art.

In particular, a task of the present invention is to make available aliquid fuel portable heater able to operate independently of the mainselectricity grid, and which at the same time has extremely limiteddimensions and weight, making it easy to move.

Another purpose of the present invention is to provide a liquid fuelportable heater comprising an electric pump for supplying the fuel,controlled so as to greatly reduce the electricity absorbed by the pump,at the same nebulisation pressure of the fuel.

A further purpose of the present invention is to provide a liquid fuelportable heater which despite comprising an oversized fuel pump withrespect to the required flow rate, makes it possible to reduce or avoidthe work in excess of the pump, thus the excess energy consumptioncorresponding to the difference between the nominal flow of the pump andflow required by the nebulizer.

Another aim of the invention is to provide a liquid fuel portable heatercomprising an electric pump for fuel supply, able to avoid the need todivert part of the flow of fuel in excess of that required forcombustion, even when the pump is oversized.

According to another aspect, the purpose of the present invention is toprovide a method for controlling the power supply of an electric pumpfor a liquid-fuelled, portable heater, so as to reduce the energyconsumption of the pump, adapting such consumption to the actual flow ofliquid fuel required by the nebulizer, even in the case in which saidpump is oversized.

These and further purposes and advantages are achieved by means of aliquid fuel portable heater according to claim 1 comprising a combustionchamber and an electric pump having an inlet for taking the fuel from atank and an outlet for sending the liquid fuel to a nebulizer in inputto the combustion chamber.

Said portable heater comprises an electric control unit configured sothat when the heater is on, said control unit actuates the electric pumpby supplying it with a sequence of pulses with a non-zero voltage, andpause intervals with a substantially zero voltage alternating with saidpulses, wherein the average duration of the pulses is less than theaverage duration of the pause intervals.

This provision makes it possible to reduce the amount of electricityabsorbed for the same amount of fuel actually conveyed to the combustionchamber.

In this regard, one can define duty cycle as the percentage of areaunder the curve of the power supply voltage of the pump in the operativeinterval of the heater, or over a period in the case of periodic powersupply, compared to the total area which would be under the curve if thepump were supplied with a constant voltage equal to the maximum value ofthe power supply voltage over the entire operative interval or period ofthe heater.

In other words, the work cycle, or duty cycle, can also be seen as theratio of the duration of ON with respect to the time interval ofoperation of the heater.

In the case of a standard frequency power supply such as 50 Hz, theaverage duration of the pulses, or ON duration is roughly equal to theaverage duration of the pause intervals or OFF duration, the pump thushaving a duty cycle of 50%.

The energy absorbed by the pump is proportional to the value of the dutycycle.

Consequently by reducing the ON duration compared to the OFF durationover the same period, or same operative interval of the heater, thevalue of the duty cycle and thus the electricity absorbed by the pump inthe unit of time is reduced.

According to one embodiment, the control unit is configured to adjustthe frequency of the sequence of actuation intervals or pulses of thepump, especially at frequency values below 50 Hz.

This provision makes it possible to reduce the number of ON portions aswell as the duration of the single supply portions for the number ofpauses, further reducing the area under the power supply curve of thepump and thus further reducing the electricity absorbed by the pump. Inother words, the reduction of electricity absorbed by the pump during anoperative interval of the heater is the result of a combined action of areduction of the average duration of the pulses or supply portionscompared to the average duration of pauses, and a reduction in thefrequency of the pulses.

Tests conducted on a standard pump suitable to be powered at 50 Hz andwith a duty cycle of 50%, showed optimal operating and energy-savingresults adjusting the frequency to 10 Hz and adjusting the ON durationto achieve a 12% duty cycle. In such conditions the electricityconsumption of the pump was reduced from 24 W, in normal operation at 50Hz and 50% duty cycle, to 5.7 W, thus leading to substantial energysavings.

This high energy saving, also taking into account the energyrequirements of the other electrical devices on board needed to operate,has the material effect of at least doubling the operation autonomy ofthe heater, if running on batteries, or halving of the number ofthermoelectric generation cells needed.

According to one embodiment, the control unit is configured to modulatethe ON duration compared to the OFF duration over each period, and thusto modulate the duty cycle, and additionally or alternatively, to alsomodulate the frequency of the power supply sequence of the pump overtime, in order to provide the correct flow of liquid fuel to thenebulizer at a pressure not below a predefined minimum threshold ofnebulisation pressure.

For example, said minimum predefined nebulisation pressure threshold maybe about 8 bars. Such pressure value guarantees a correct nebulisationby the nebulizer.

This way the problem of having to divert a portion of excess fuelgenerated by an oversized pump to bring it back to the tank is resolved.In fact by adjusting the duty cycle and frequency the pump is poweredonly when and as required to ensure a flow and pressure to the nebulizersufficient for said nebulisation. No overworking is produced, no excesselectricity is wasted unnecessarily.

According to one embodiment, the heater according to the inventioncomprises an expansion chamber for pressure waves, positioned betweenthe pump outlet and the nebulizer in order to store excess fuel inoutput from the pump and release it gradually to the nebulizer at apressure not below a predefined minimum threshold of nebulisationpressure.

Advantageously, the expansion chamber acts as a real volumetric temporalreserve of pressurised fuel simultaneously performing two technicaltasks.

In fact, according to a first advantageous aspect said expansion chamberacts as a reserve and accumulator of the excess flow of fuel dispensedby the pump in the active ON phase, enabling the continuous dispensingof fuel toward the nebulizer during the off phase of the pump.

According to another advantageous aspect, the expansion chamber acts asa pressure equalizer, thus as a regulator of pressure peaks in thecircuit downstream of the pump.

According to another aspect of the invention, the aforesaid purposes andadvantages are satisfied by a method for controlling an electricitysource for an electric fuel pump of a portable liquid fuel heater bymeans of an electric control unit configured to control the electricitysource, said method comprising a step of electrically powering saidpump, with the heater ON, with a sequence of pulses with a non-zerovoltage, and pause intervals with a substantially zero voltagealternating with said pulses, wherein the average duration of the pulsesis less than the average duration of the pause intervals.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will, inany case, be evident from the description given below of its preferredembodiments, made by way of a non-limiting example with reference to theappended drawings, wherein:

FIGS. 1 and 2 show two voltage waveforms at fixed frequency for poweringan electric pump for a heater, according to the prior art;

FIG. 1A shows a typical pressure-flow trend of an electric pump;

FIGS. 3, 4 and 5 show details of voltage supply trends for an electricpump for a heater, according to the present invention;

FIG. 6 shows a schematic view of a heater according to the invention;

FIG. 7 is a block diagram of the heater in FIG. 6.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS

With reference to the figures, reference numeral 100 globally denotes aliquid fuel portable heater according to the invention.

In this description, the pulse sequence of the pump power supply is alsosequence of power intervals, or sequence of ON.

Consequently the duration of the pulse is the duration of the powerinterval and also the ON duration.

Similarly, the pause intervals are also called non-powered intervals orOFF intervals.

In addition, the interval in which the heater is switched on and thusthe interval during which liquid fuel is dispensed from the nebulizerinto the combustion chamber and in which combustion takes place willalso be referred to as the heater operative interval,

In this description, the liquid fuel is sometimes referred to as fuel.

The heater 100 comprises a combustion chamber 101, for example of asubstantially tubular shape, into which a liquid fuel, or fuel, such asdiesel fuel, in the form of aerosol 15, in particular as a nebulisedmixture of fuel and air, is conducted.

The heater 100 thus comprises a nebulizer 13 to form the fuel aerosoland to continuously nebulise it into the combustion chamber 101, inwhich a flame 16 is generated. Nebulisation is performed upon reaching apredefined fuel pressure upstream of a nebulizer nozzle.

Outside and around the combustion chamber a casing 102, or skirt, may bepresent forming an interspace 103 around the combustion chamber 101,suitable to be crossed by a flow of air 104 which thermally insulatesthe combustion chamber from the outer casing, and simultaneously heatsand forcibly enters an environment to be heated.

To form such forced flow of air 104 a fan 105 placed upstream of thenebulizer 13 and interspace 103 may be used. Part of said flow may bediverted into the combustion chamber 101 to provide combustion air forcombustion.

The fan 105 is driven by an electric motor 105′.

According to one embodiment, the heater comprises a tank 6 placed onboard the heater, in particular under the combustion chamber housing 101or casing 102.

A frame, not shown in the drawings connects and joins all the componentsof the heater 100, so as to move it easily in one body.

The heater may comprise wheels 7 positioned to facilitate its movement.

The heater 100 further comprises an electric pump 10 having an inlet 11for receiving the fuel from the tank 6, and an outlet 12 to send saidliquid fuel to the nebulizer 13 in input to the combustion chamber 101.

As shown in FIG. 7, the heater comprises a supply duct 43 of the fuelwhich connects the tank 6 to the pump 10, to transfer to the pump 10 thefuel 44 contained in the tank 6.

A supply duct 45 fluidically connects the pump 10 to the nebulizer 13.

A compensation duct 46 fluidically connects the supply duct 45 to theexpansion chamber 14.

According to one embodiment, the heater 100 further comprises anelectricity source 24, in particular mounted on board and thusintegrated in the heater. This electricity source is dimensioned tosupply electricity to all the electrical components on board, such asthe pump 12, a control unit, a motor 105′ of the fan 105, circuitboards, solenoid valves.

According to one embodiment, the electricity source is an electricbattery, or storage battery for example a rechargeable battery.

According to one embodiment, the heater 100 comprises at least onedirect conversion cell of a temperature differential into electricenergy (not shown) mounted on the heater 100 to receive a temperaturedifferential between the inside of the combustion chamber and theoutside environment, in which said electricity produced by said at leastone conversion cell is suitable to electrically power said electric pumpand said control unit 20.

For example, the at least one direct conversion cell is a Seebeck cell.

According to one embodiment the heater comprises a Stirling motorpositioned to take the temperature differential between the combustionchamber and the environment and convert it into mechanical energy, forexample to drive an electricity generator.

The heater 100 comprises a control unit 20 configured to power theelectric pump, or control an electricity supply of the pump, with theheater on, with a sequence of pulses 115, 115′ with a non-zero voltage,and pause intervals 116 with a substantially zero voltage alternatingwith said pulses, wherein the average duration of the pulses 115, 115′is less than the average duration of the pause intervals 116. Inparticular, such average durations are evaluated for the same operativeinterval of the heater.

According to an embodiment, the average duration of the pulses 115, 115′is preferably less than ⅔ of the average duration of the pause intervals116, or, even more preferably less than half the average duration of thepause intervals 116.

In this context, the average duration of the pulses is understood as thequotient of the sum of the durations of all the pulses and the totalnumber of pulses in the operative interval of the heater.

Similarly, the average duration of the pause intervals is understood asthe quotient of the sum of the durations of all the pause intervals andthe total number of pauses in the operative interval of the heater.

In other words, the control unit 20 is configured to control anelectricity supply of the electric pump 10, with the heater on, in asequence of power intervals 115 having an ON duration of T1, andnon-powered intervals 116 having an OFF duration of T2, wherein the sumof the durations of the ON intervals T1 is less than the sum of thedurations of the OFF intervals T2 in the operative interval of theheater.

Some possible examples of voltage trends V as a function of time t topower the pump 10, according to the invention, are shown in FIGS. 3, 4and 5, while FIGS. 1 and 2 show possible electric voltage trends as afunction of time using a traditional power supply. Along the x-axis 121is the time, and along the y-axis 122 the electrical voltage is shown.

In particular, the prior trend shown in FIGS. 1 and 2, with a sinusoidalwaveform in FIG. 1 and with a square waveform in FIG. 2, is at fixedfrequency and maximum constant voltage, for example at 50 Hz and has aduty cycle of approximately 50%.

The provision of reducing the on duration compared to the OFF timereduces the duty cycle and thus the electricity absorbed by the pumpcompared to that traditionally used.

In other words, according to an embodiment, the control unit 20 isconfigured to adjust, or modulate, the ON duration compared to the OFFduration to obtain a duty cycle of less than 50%.

In other words again the duty cycle value, or percentage value of theintegral of a voltage/time curve of said sequence of pulses in anoperative interval of the heater with respect to the integral of ahypothetical voltage/time curve with a direct, constant voltage, with anamplitude equal to the maximum amplitude of said voltage/time curve ofsaid sequence of pulses in the same operative interval of the heater, isless than 50%.

According to an embodiment, the control unit 20 is configured to adjust,or modulate, the ON duration compared to the OFF duration, or, in otherwords, the duration T1 of the pulses compared to the duration T2 of thepause intervals, to obtain a duty cycle, with a value of less than 40%,in particular less than 30%, for example less than 20%. Experimentaltests have shown particularly favourable behaviour of the pump at suchvalues of the duty cycle.

According to an embodiment, the control unit 20 is configured to adjust,or modulate, the ON duration compared to the OFF duration to obtain aduty cycle, with a value between 10% and 40%, for example between 20%and 30%.

According to a preferred embodiment, the control unit 20 is configuredto perform a duty cycle of about 12%. At this value of duty cycle, ithas been found that the power absorbed by the pump, althoughadvantageously greatly reduced in value, allows the supply of anadequate fuel flow and pressure for nebulisation through the nebulizer13.

According to an embodiment, the control unit 20 is configured to adjustthe frequency of the sequence of actuation intervals of the pump 210,211, 212 in the operative interval of the heater, especially atfrequency values below 50 Hz.

This makes it possible to further reduce the power absorbed by the pump10. In fact, reducing the frequency of the supply portions, or sequenceof pulses, means further reducing the area under the curve in theoperative interval of the heater and thus reducing the energy absorbedby the pump. Said reduction of the frequency, in conjunction with thereduction in the average duration of the pulses compared to the averageduration of pause intervals, allows very high energy savings to beachieved.

According to an aspect of the invention, the control unit is configuredto adjust, or reduce the frequency of the pulse sequence, to valuesbetween 10 Hz and 40 Hz, for example between 10 Hz and 30 Hz, preferablyto about 10 Hz. Experimental tests have shown particularly advantageousresults in terms of energy saving by reducing the frequency of the pulsesequence to the above values. In fact in said pulse frequency ranges, inconjunction with the reduction in the average duration of the pulsescompared to the average duration of the pause intervals, there is anevident reduction of electricity consumption while continuing to providea fuel flow and pressure suitable for proper operation of the heater.

The optimum operating conditions occur at a supply frequency ofapproximately 10 Hz. In such conditions the power absorbed by the pumpis minimal but still permits the supply of a fuel pressure to thenebulizer, above the minimum nebulisation pressure, thus permitting anoptimal nebulisation.

Such duty cycle and frequency values can be modulated jointly orseparately, this way it is possible to achieve the best performancebalance in relation to the type of pump used, with the least consumptionof electricity.

However, the combination thereof permits the maximum energy saving.

In fact, a pump suitable to be powered at a frequency of 50 Hz with aduty cycle of 50% resulting in a power consumption of 24 W, is stillable to provide sufficient flow and pressure of the fuel to thenebulizer if powered at a frequency of 10 Hz with a duty cycle of 12%,leading to the optimal result of a consumption of just 5.7 W. This is anenergy saving so high that it doubles the power reserve of the heater ifrunning on battery, or halves the size if powered by a Seebeck cell.

According to an embodiment, the control unit 20 is configured tomodulate the ON duration T1 compared to the OFF duration T2 of eachperiod T so as to provide sufficient liquid fuel to the nebulizer 13 ata pressure not lower than a predefined minimum threshold of nebulisationpressure.

In particular, said minimum threshold is about 8 bar.

According to an embodiment, the control unit 20 is configured tomodulate the frequency of said sequence 210, 211, 213 in the time unitso as to supply the liquid fuel to the nebulizer 13 at a pressure notlower than said predefined minimum threshold of nebulisation pressure.

According to an embodiment, the control unit 20 is configured to varyover time the duration of the individual power intervals having an ONduration T1, and the ratio between the duration of each power intervaland an OFF duration T2 of the interval that precedes and/or follows thepower interval, and/or to vary the frequency of said sequence 210, 211,213 over time, for example in a differentiated manner from one period toanother, for example to compensate for any variations in the flow demandby the nebulizer and any variations in the flow, in order to ensure auniform and constant flame over time.

According to an embodiment, the control unit 20 comprises a closed loopcontrol with feed-back on the fuel pressure measured upstream of thenebulizer. In this case the control unit is configured to automaticallymodulate the ON duration T1 and OFF duration T2 of each period T, and tomodulate the frequency of the actuation intervals in the unit of time,so that the pressure measured upstream of the nebulizer is substantiallyequal to a predefined set-point value, for example not less than thepredefined minimum threshold of nebulisation pressure.

Furthermore, according to an embodiment, the heater 100 may comprisepressure sensors, or pressure gauges 39 arranged to detect the pressurevalue of the fuel upstream of the nebulizer, and, for example, to sendthe corresponding information to the closed loop control.

Alternatively, the control unit 20 comprises an open control in whichthe minimum nebulisation threshold value is mechanically set by thecharacteristics of the nebulizer. In this case the nebuliser permitsnebulisation only above said minimum threshold and does not permitnebulisation below said minimum threshold.

According to an embodiment the nebulizer 13 comprises a calibratedpressure non-return valve 17, for example at the minimum threshold valuefor nebulisation, and a calibrated nozzle 18.

This way the nebulizer valve 17 opens only when it reaches the minimumnebulisation threshold. Such a nebulizer prevents the involuntaryleakage of fuel when the pressure at the nebulizer is less than theminimum threshold for nebulisation. This makes for considerable safetyin use.

According to an embodiment, the power interval 115 is formed of a singlepulse to perform a pumping cycle, or the power interval 115 is formed ofplurality of successive electrical pulses close together to perform acorresponding plurality of pumping cycles. In particular, FIG. 3 showsan example of a power interval 115 consisting of a single electricalpulse 115′, while FIGS. 4 and 5 show examples of a power interval 115consisting of 3 pulses 115′.

In other words, the sequence of pulses to power the pump may comprise aplurality of successive electrical pulses 115′ close together, forexample, to perform a corresponding plurality of pumping cycles.

In general a number of pulses may be used such as to generate a flowrate and fuel pressure such as to permit a continuous and uniformnebulisation to the nebulizer.

According to an embodiment, said or each pulse of said power interval115 may be in the form of a sinusoidal waveform or a square waveform.

According to an embodiment, the pump 20 is a reciprocating pump such asa piston.

According to an embodiment, such piston pump comprises a cylinder and apiston sliding inside the cylinder so as to push out the fuel in apulsed manner towards the nebulizer. Outside the cylinder a solenoid iswound which, when crossed by electric current, generates anelectromagnetic field which moves the piston between a first and asecond end stroke position. In the movement from the first end strokeposition to the second end stroke position the piston pump sucks thefuel from the tank, while in the opposite stroke, from the second endstroke position to the first end stroke position it pushes the fuel tothe nebulizer 13.

In a preferred embodiment, the piston pump comprises a spring configuredto return the piston from the first end stroke position to the secondend stroke position at the end of the dispensing phase.

In other words, such a piston pump provides for an active phase in whichthe solenoid is electrically powered, in which the piston moves from thesecond end stroke position to the first end stroke position, pushing thefuel to the nebulizer under pressure, and a passive return phase inwhich the piston moves backwards from the first end stroke position tothe second end stroke position, in which the solenoid is not powered andthe spring returns the piston to the second end stroke positionperforming the suction phase of the fuel.

With reference to FIGS. 3 and 4 showing the voltage trend applied to thepump, in this case to the solenoid, the active phase is represented bythe portion of the pulse 115′ ranging from the minimum value of thepotential, or voltage, to the maximum value of the potential, orvoltage, and by the portion, while the passive phase corresponds to thepulse portion 115′ which goes from the maximum value to the minimumvalue of the potential.

According to an alternative embodiment, the pump 10 may be areciprocating pump diaphragm, so as to compensate abrupt pressurevariations.

Again in an alternative embodiment, the pump 10 may for example be agear or vane rotary pump. In this case, an example of a power supplyvoltage trend of the pump is shown in FIG. 5.

In general, the pump 10 may comprise an electrical actuator 10″ and amechanical pumping apparatus 10′ mechanically connected to the actuator10″ so that said actuator 10″ operates the mechanical pumping apparatus10′ to pump the fuel.

The electric actuator 10″ transforms the incoming electricity intomotion which is provided to the pumping apparatus.

The pumping apparatus 10′ is selected from the normal existing types ofdevices such as piston, diaphragm, gear, vane.

The control unit 20, according to an embodiment of the invention,comprises a current controller 31 and a timer 32, wherein said currentcontroller 31 is configured to generate in output said power interval115 having an ON duration T1, for example having a square or sinusoidalwaveform, for example said power interval comprising a single pulse 115′or a plurality of pulses 115′ side by side and close to each other, andwherein said timer 32 adjusts said pause interval 116, or OFF interval,having an OFF duration T2.

According to an embodiment, the heater 100 comprises a switch 33electrically interposed between the electricity source 24 and theelectric pump 10, and in addition or alternatively, between theelectricity source 24 and the control unit 20. For example the switch 33is arranged to allow/prevent the power supply of the pump 10 and thecontrol unit 20 simultaneously.

According to an embodiment, the control unit 20 and the switch 33 areintegrated on the same circuit board 37.

According to an embodiment, the heater 100 further comprises electroniccontrol devices 34, 35 to control further electrical devices 36′, 36″,36′″ placed on board the heater, such as fans 105 to generate a forcedflow of air, or solenoid valves for the fuel.

According to an embodiment, said electronic control devices 34, 35 areintegrated on said circuit board 37.

According to an embodiment, the heater comprises an expansion chamber 14in fluidic communication with the fuel between the outlet 12 of the pump10 and the nebulizer 13. Said expansion chamber 14 is suitable to storeexcess fuel gradually with respect to a fuel flow actually passingthrough the nebulizer during the powering of the pump at the electricalpulses 115. Likewise, the expansion chamber is suitable to graduallyrelease the excess fuel to the nebulizer 13 during the pause intervals,providing a continuous delivery of fuel through the nebulizer during anentire operative interval of the heater.

The predefined minimum threshold of nebulisation is for example about 8bar.

According to an embodiment, the expansion chamber 14 is a closed chamberof variable internal volume in fluidic connection with the pressurisedfuel upstream of the nebulizer 13, suitable to expand containing alarger amount of fuel when the fuel pressure increases, and suitable tobe compressed to release said fuel when the pressure decreases.

According to an embodiment, the heater comprises a rigid container 51divided into two variable volume chambers, of which a first chamber 52is formed of said expansion chamber 14, and a second chamber 53 containsa compressible material, such as a gas, so that when the expansionchamber 14 expands, said second chamber 53 is compressed accordingly, inparticular exerting an additional pressure against the expansion chamber14.

In other words the expansion chamber 14 serves as a temporal volumetricreserve of pressurised fuel performing two tasks together.

In fact, said expansion chamber 14 performs a first task acting as aflow equalizer, i.e. as a deposit and reserve of the excess flow of fueldispensed by the pump in the active ON phase, enabling the continuousdispensing of fuel towards the nebulizer during the OFF phase of thepump.

In addition, said expansion chamber 14 performs a second task by actingas a pressure equalizer, i.e. damping the pressure peaks in the fuelcircuit downstream of the pump.

The presence of said expansion chamber 14 compensates a possiblefluctuating trend of peaks and dips of the fuel pressure downstream ofthe pump, due to the alternate operation of the pump, for example of thepiston pump. This way, moreover, the risk of non-nebulisation andconsequent involuntary extinguishing of the heater is avoided. Thepresence of the expansion chamber also makes it possible to avoid thephenomenon known as “pipe hammer” inside the fuel ducts in the portionbetween the pump and the nebulizer, caused by the rapid pressure dropoccurring at the end of the active phase of powering the pump.

When the pump 10 is started, the fuel fills the expandable container upto a minimum nebulisation threshold value at which the nebulizer works,after which the fuel begins to flow from the nebuliser. At each pulse ofthe pump, a first part of the volume of fuel contained in the expandablecontainer flows through the nebulizer, and a second part of said volumeis stored in the expandable container in order to ensure the flow in theOFF phase.

According to another aspect of the present invention, the aforesaidpurposes and advantages are achieved by a method for controlling thepower supply of an electric pump for a liquid fuel portable heater.

The method for controlling an electric power supply of an electric fuelpump 10 for a liquid fuel portable heater by means of an electriccontrol unit 20 configured to power the pump, comprises a step ofcontrolling said power supply, with the heater on, with a sequence ofpulses 115, 115′ with a non-zero voltage, and pause intervals 116 with asubstantially zero voltage alternating with said pulses, wherein theaverage duration of the pulses 115, 115′ is less than the averageduration of the pause intervals 116.

According to an embodiment, the method comprises a step of adjusting theduty cycle value, or percentage value of the integral of a voltage/timecurve of said sequence of pulses in an operative interval of the heaterwith respect to the integral of an hypothetical voltage/time curve witha direct, constant voltage with a amplitude equal to the maximumamplitude of said voltage/time curve of said sequence of pulses in thesame operative interval of the heater, so that said duty cycle value isless than 50%.

In particular, the on duration T1, or pulse duration, and the offduration T2, or duration of the pause interval, are chosen so as toensure a continuous supply of fuel to the nebulizer.

A step of adjusting the frequency of said sequence of pulses 115, 115′so that said frequency of the sequence is less than 50 Hz.

According to an embodiment, the method comprises a step of modulatingthe ON duration T1 compared to the OFF duration T2 of each period T soas to provide the liquid fuel to the nebulizer 13 at a pressure notlower than a predefined minimum threshold of nebulisation pressure.

According to an embodiment, the method comprises a step of modulatingthe frequency of said sequence of pulses in the time unit so as tosupply the liquid fuel to the nebulizer 13 at a pressure not lower thansaid predefined minimum threshold of nebulisation pressure.

According to an embodiment, the control method comprises a step ofvarying over time the duration of the pulses with respect to theduration of the pause intervals, so as to supply the liquid fuel to thenebulizer 13 at a pressure not less than a predefined minimum thresholdof nebulisation pressure.

According to an embodiment the control method comprises a step ofvarying over time the frequency of the sequence of pulses so as tosupply the liquid fuel to the nebulizer 13 at a pressure not less than apredefined minimum threshold of nebulisation pressure.

A person skilled in the art may make modifications and adaptations tothe embodiments of the device described above, replacing elements withothers functionally equivalent so as to satisfy contingent requirementswhile remaining within the sphere of protection of the following claims.Each of the characteristics described as belonging to a possibleembodiment may be realised independently of the other embodimentsdescribed.

1. A liquid fuel portable heater (100), comprising: a combustion chamber(101) having a fuel inlet with a nebulizer (13); an electric pump (10)having an inlet (11) for suctioning said liquid fuel from a tank (6),and an outlet (12) connected to said nebulizer (13) to bring the liquidfuel to the nebulizer (13); an electric control unit (20) configured sothat, when the heater (100) is turned on, said control unit (20)actuates the electric pump by supplying it with a sequence of pulses(115, 115′) with a non-zero voltage, and pause intervals (116) with asubstantially zero voltage alternating to said pulses, wherein theaverage duration of the pulses (115, 115′) is less than the averageduration of the pause intervals (116).
 2. The portable heater accordingto claim 1, wherein the duty cycle value, or percentage value of theintegral of a voltage/time curve of said sequence of pulses (115, 115′)in an operative interval of the heater (100), with respect to theintegral of a hypothetical voltage/time curve with a direct, constantvoltage, with a amplitude equal to the maximum amplitude of saidvoltage/time curve of said sequence of pulses (115′, 115) in the sameoperative interval of the heater, is less than 50%.
 3. The portableheater according to claim 1, wherein said control unit (20) isconfigured to adjust a frequency of said sequence of pulses (115, 115′),so that said frequency is less than 50 Hz.
 4. The heater according toclaim 1, wherein said control unit (20) is configured so as to vary overtime the duration (T1) of the pulses with respect to the duration (T2)of the pause intervals, so as to provide the liquid fuel to thenebulizer (13) at a pressure that is not less than a predeterminedminimum threshold of nebulisation pressure.
 5. The heater according toclaim 1, wherein said control unit (20) is configured to vary over timethe frequency of the sequence of pulses (115, 115′) so as to provide theliquid fuel to the nebulizer (13) at a pressure that is not less than apredetermined minimum threshold of nebulisation pressure.
 6. The heateraccording to claim 1, wherein said sequence of pulses (115, 115′)comprises a plurality of electric pulses (115′) that are successive andclose together, in particular to carry out a corresponding plurality ofpumping cycles.
 7. The heater according to claim 1, comprising anexpansion chamber (14) in flow communication with the liquid fuel,interposed between the outlet (12) of said pump (10) and said nebulizer(13), said expansion chamber (14) being configured to store an excessamount of liquid fuel with respect to a flow rate of liquid fuel passingthrough the nebulizer, said excess amount of liquid fuel being generatedduring an electric power supply of the pump at the electric pulses(115), and being configured to gradually release said excess amount ofliquid fuel to the nebulizer (13) during the pause intervals (116),providing a continuous dispensing of liquid fuel through the nebulizerduring an entire operative interval of the heater.
 8. The heateraccording to claim 1, comprising at least one conversion cell (95) forthe direct conversion of a temperature differential into electric power,said at least one conversion cell (95) being mounted at the heater (100)to receive a temperature differential between the combustion chamber(101) and the outer environment, said at least one conversion cell (95)being connected to electrically supply said electric pump and saidcontrol unit (20).
 9. A method for controlling an electric power supplyof a fuel electric pump (10) of a liquid fuel portable heater by anelectric control unit (20) configured to control said electric powersupply, said method comprising a step of electrically supplying saidpump, once the heater is turned on, with a sequence of pulses (115,115′) with a non-zero voltage, and pause intervals (116) with asubstantially zero voltage alternating to said pulses, wherein theaverage duration of the pulses (115, 115′) is less than the averageduration of the pause intervals (116).
 10. The method according to claim9, comprising a step of adjusting the duty cycle value, defined as thepercentage value of the integral of a voltage/time curve of saidsequence of pulses (115, 115′) in an operative interval of the heater(100), with respect to the integral of an hypothetical voltage/timecurve with a direct, constant voltage with an amplitude equal to themaximum amplitude of said voltage/time curve of said sequence of pulses(115, 115′) in the same operative interval of the heater, so that saidduty cycle value is less than 50%.
 11. The method according to claim 9,comprising a step of adjusting the frequency of said sequence of pulses(115, 115′), so that said frequency of the sequence is less than 50 Hz.12. The method according to claim 9, comprising a step of varying overtime the duration of the pulses (115, 115′) with respect to the durationof the pause intervals (116), and/or varying over time the frequency ofthe sequence of pulses (115, 115′) so as to provide the liquid fuel tothe nebulizer (13) at a pressure 20 that is not less than apredetermined minimum threshold of nebulisation pressure.